Two frame structure types, i.e., frame structure type 1 and frame structure type 2, are defined in current Long Term Evolution (LTE) system. Frame structure type 1 is used in a Frequency Division Dual (FDD) structure, while frame structure type 2 is used in a Time Division Dual (TDD) structure.
FIG. 1 is a schematic diagram of the composition of frame structure type 1 in the existing LTE system. As shown in FIG. 1, each radio frame is 10 ms long and consists of 10 subframes of length 1 ms. Furthermore, each subframe includes two timeslots, and the time length of a timeslot is 0.5 ms.
FIG. 2 is a schematic diagram of the composition of frame structure type 2 in the existing LTE system. As shown in FIG. 2, each radio frame of length 10 ms consists of two half-frames of length 5 ms each. Each half-frame consists of five subframes of length 1 ms. The second subframe of each half-frame is a subframe with three special timeslots, as shown in FIG. 2, including downlink pilot timeslot (DwPTS), guard period (GP) and uplink pilot timeslot (UpPTS). Each of the other subframes includes two timeslots of length 0.5 ms.
Meanwhile, five random access burst structures are defined for the LTE system. A user equipment (UE) can use the five random access burst structures to initiate, on its corresponding random access channel, a random access procedure to a base station of a cell where the UE locates. Parameters corresponding to each of the five random access burst structures are as shown in Table 1, wherein Ts=1/(15000*2048)s.
TABLE 1Parameters corresponding to each of the five random access burst structuresBurststructureTime lengthTCPTSEQSequence lengthGT01ms 3152 × Ts24576 × Ts839≈97.4us12ms21012 × Ts24576 × Ts839≈516us22ms 6224 × Ts2 × 24576 × Ts839≈197.4us(transmit twice)33ms21012 × Ts2 × 24576 × Ts839≈716us(transmit twice)4≈157.3us 448 × Ts 4096 × Ts139≈9.4us
Here, burst structure 4 can only be used within an uplink pilot timeslot of frame structure type 2, while burst structures 0-3 can be transmitted in normal subframes of frame structure type 1 and frame structure type 2.
FIG. 3 is a schematic diagram of an existing random access burst structure. As shown in FIG. 3, each random access burst structure has three parts including Cyclic Prefix (CP), Sequence and Guard Time (GT). CP is mainly used for guaranteeing frequency domain sounding at receiving side, while GT is mainly used for avoiding interference, which may be caused due to time uncertainty of a random access channel, on normal data subframes subsequence to the random access channel.
In the uplink of an LTE system, there are an uplink shared channel and an uplink control channel, and also an uplink channel quality sounding pilot, of which positions are shown in FIG. 4. The uplink control channel distributes symmetrically on two sides of the frequency band of an uplink subframe, which is illustrated in FIG. 4 in slash; the middle part of the frequency band of the uplink subframe shown in FIG. 4 in blank is the uplink shared channel, wherein the area in black is the uplink channel quality sounding pilot. Meanwhile, one or more random access channels can be located in an uplink pilot timeslot (other two timeslots, i.e., DwPTS and GT, are not indicated in FIG. 4) and normal subframes, wherein the normal subframes refer to such as subframe 2, subframe 3 and subframe 4 illustrated in FIG. 4. These random access channels, whose specific frequency domain positions are designated by a base station, distribute randomly within the whole frequency band.
When a random access channel is located in a normal subframe, a random access burst structure configured for the channel can be any of random access burst structures 0-3 as shown in Table 1. These random access burst structures have relatively long length. Accordingly, lengths of CP and GT parts are long, which are usually longer than that of an Orthogonal Frequency Division Multiplexing (OFDM) symbol. As such, when an uplink channel quality sounding pilot of a UE and a random access channel are located in the same frequency, it is allowable for the uplink channel quality sounding pilot and the CP or GT part of the random access channel to be overlapped in frequency domain since the uplink channel quality sounding pilot merely occupies an OFDM symbol. That is, a random access signal and an uplink channel quality sounding pilot can be transmitted in the same frequency at the same time. Since the existence of an uplink channel quality sounding pilot has no impact on Sequence part of a random access burst structure, the detection performance of a random access channel will not be affected.
However, under some circumstances, frequency hopping can be applied for an uplink channel quality sounding pilot of a UE according to certain configuration. That is, the uplink channel quality sounding pilot of the UE does not have fixed time-frequency position in different time, and it may be located in different subframe. Then, at a time, the time-frequency position of the uplink channel quality sounding pilot may overlap with a random access channel located in an uplink pilot timeslot of frame structure type 2. Since the only random access burst structure the random access channel located in the uplink pilot timeslot can use is random access burst structure 4 which has a relatively short length, i.e., merely two OFDM symbols, wherein CP or GT part has a length less than one OFDM symbol, there may be a conflict between the random access channel and the uplink channel quality sounding pilot. In this case, the detection performance of the random access channel will be affected if a random access signal and an uplink channel quality sounding pilot are transmitted in the same frequency at the same time. Although a multiplexing method has been proposed in the prior art for solving this problem, a complicated multiplexing configuration for a random access channel and time-frequency position of an uplink channel quality sounding pilot is needed in this method, which is not convenient to implement. Therefore, it is not an ideal way to solve this problem.